The synthesis of analogs of adenosylcobalamin containing a thiol functionality in close proximity to the 5'-methylene carbone. Photolysis of these analogs may mimic the adenosylcobalamin-dependent enzymic reactions. The synthesis of analogs of adenosylcobalamin in which the sugar moiety is replaced by a methyoxyethyl or a 1,5-didioxyribitol group. These analogs incorporate most of the properties of the ribose moiety and may be very potent inhibitors of the adenosylcobalamin-dependent reactions. The purification and characterization of ribonucleotide reductase, thioredoxin and thioredoxin reductase from Corynebacterium nephridii. It is proposed to study the physical and chemical properties of these proteins, the first two of which have been purified to homogeneity. The purification and characterization of methylmalonyl CoA mutase from Ascaris lumbricoides.